An internal combustion engine conventionally comprises an engine block including one or more cylinders, and a cylinder head attached to the cylinder block to close the top of the cylinders. The engine block and the cylinder head are generally formed as aluminum or iron castings. Each of the cylinders accommodates a piston that cooperates with the cylinder head to define a combustion chamber. A fuel and air mixture is disposed in the combustion chamber and ignited, resulting in hot expanding exhaust gasses causing reciprocating movement of the piston. The fuel may be provided through a fuel injector, which injects the fuel directly into the combustion chamber. The pistons are mechanically coupled to a crankshaft, so that the reciprocating movement of the pistons is converted into a rotation of the engine crankshaft.
Each of the cylinders is equipped with at least an intake valve and an exhaust valve, which are actuated by a camshaft rotating in time with the crankshaft. These valves selectively allow the air into the combustion chamber from at least an intake port, and alternately allow the exhaust gases to exit through at least an exhaust port. The intake ports and the exhaust ports are internally defined by the cylinder head.
The air may be distributed to the intake ports through an intake manifold, which is conventionally attached to the cylinder head. The intake manifold is typically formed from aluminum or plastic and includes runner portions in communication with each of the intake ports of the cylinder head. The intake manifold further includes a collector volume, in communication with each of the intake runner portions and with an intake pipe that conveys air from the ambient environment to the collector volume.
The exhaust gases from the combustion chamber may be collected in an exhaust manifold, which is conventionally attached to the cylinder head at the opposite side of the intake manifold. The exhaust manifold is typically formed from stainless steel or cast iron and includes runner portions in communication with each of the exhaust ports of the cylinder head. The exhaust manifold further includes a collector volume, in communication with each of the exhaust runner portions and with an exhaust pipe that conveys the exhaust gases from the collector volume to the ambient environment. One or more aftertreatment devices, typically catalytic aftertreatment devices such as a Diesel Oxidation Catalyst (DOC) and others, are usually located in the exhaust pipe to reduce the pollutant emissions of the internal combustion engine. In order to reduce the footprint of the internal combustion engine, cylinder heads have been recently designed wherein the exhaust manifold, i.e. the exhaust runner portions and the collector volume, is internally defined by the cylinder head itself to form an integral exhaust manifold.
Many internal combustion engines are also equipped with a turbocharger having the function of increasing the pressure of the air entering the engine cylinders, in order to enhance the engine torque. The turbocharger conventionally comprises a bearing housing, which accommodates a rotating shaft, also referred as turbocharger shaft, and the bearings thereof. The bearing housing is generally formed as an aluminum or iron casting. The opposite ends of the turbocharger shaft jut out from the bearing housing. A turbine wheel is fixed to one end of the turbocharger shaft, whereas the opposite end carries a compressor wheel. The turbine wheel and the compressor wheel are respectively accommodated inside a turbine housing and inside a compressor housing, which are fastened at the opposite side of the bearing housing. The turbine housing and the compressor housing are typically formed from stainless steel or cast aluminum. The turbine housing comprises an inlet in communication with the exhaust manifold and an outlet in communication with the exhaust pipe, so that the turbine wheel rotates by receiving the exhaust gases. The compressor housing comprises an inlet in communication with the intake pipe and an outlet in communication with the intake manifold, so that the rotation of the compressor wheel, driven by the turbine wheel via the turbo-charger shaft, increases the pressure of the air in the intake manifold and then in the engine cylinders.
Generally, the entire turbocharger is carried by the turbine housing, whose inlet is defined by a rigid pipe cast in single body with the turbine housing. The free end of this rigid pipe is provided with a fastening flange that is attached directly to the exhaust manifold by means of conventional fastening techniques, such as threaded fasteners. As a matter of fact, the turbine housing is held by the exhaust manifold, whereas the bearing housing is held by the turbine housing itself and the compressor housing is held by the bearing housing. This design implies that the entire turbocharger is fixed to the exhaust manifold in a cantilever fashion, so that it may be subjected to relatively wide oscillations during the operation of the internal combustion engine, which may cause malfunctions and even damages.
In order to solve this drawback, turbochargers have been designed wherein the bearing housing comprises a pedestal having a fastening flange that may be directly fastened to the engine block. Even if this turbochargers are actually carried by the bearing housing, the inlet of their turbine housing is still connected with the exhaust manifold by means of a rigid metallic pipe. Since the exhaust gases exiting the exhaust manifold may be very hot (up to 800° C.), this connection implies that, during the operation of the internal combustion engine, the rigid metal pipe connecting the turbine housing and the exhaust manifold is heated much more than the pedestal connecting the bearing housing and the engine block, thereby causing different thermal deformations which may still be responsible of malfunctions and damages.
In view of the above, it is an object of an embodiment of the invention to provide a turbocharger that can be mounted in a more reliable way, thereby solving or at least positively reducing the above mentioned drawbacks.
Another object is that of meeting this goal with a simple, rational and rather inexpensive solution.